1. Field of the Invention
The present invention relates to a method and related apparatus for driving an LCD monitor, and more particularly, to a method and related apparatus for dynamically determining whether sub-frames are necessary to be inserted and determining gray values of the sub-frames according to a gray value difference between adjacent frames.
2. Description of the Prior Art
The advantages of a liquid crystal display (LCD) include lighter weight, less electrical consumption, and less radiation contamination. Thus, the LCD monitors have been widely applied to various portable information products, such as notebooks, PDAs, etc. In an LCD monitor, incident light produces different polarization or refraction effects when the alignment of liquid crystal molecules is altered. The transmission of the incident light is affected by the liquid crystal molecules, and thus magnitude of the light emitting out of liquid crystal molecules varies. The LCD monitor utilizes the characteristics of the liquid crystal molecules to control the corresponding light transmittance and produces gorgeous images according to different magnitudes of red, blue, and green light.
Please refer to FIG. 1, which illustrates a schematic diagram of a prior art thin film transistor (TFT) LCD monitor 10. The LCD monitor 10 includes an LCD panel 100, a control circuit 102, a data-line-signal output circuit 104, a scan-line-signal output circuit 106, and a voltage generator 108. The LCD panel 100 is constructed by two parallel substrates, and the liquid crystal molecules are filled up between these two substrates. A plurality of data lines 110, a plurality of scan lines 112 that are perpendicular to the data lines 24, and a plurality of TFTs 114 are positioned on one of the substrates. There is a common electrode installed on another substrate, and the voltage generator 108 is electrically connected to the common electrode for outputting a common voltage Vcom via the common electrode. Please note that only four TFTs 114 are shown in FIG. 1 for clarity. Actually, the LCD panel 100 has one TFT 114 installed in each intersection of the data lines 110 and scan lines 112. In other words, the TFTs 28 are arranged in a matrix format on the LCD panel 100. The data lines 110 correspond to different columns, and the scan lines 112 correspond to different rows. The LCD monitor 10 uses a specific column and a specific row to locate the associated TFT 114 that corresponds to a pixel. In addition, the two parallel substrates of the LCD panel 100 filled up with liquid crystal molecules can be considered as an equivalent capacitor 116.
The operation of the prior art LCD monitor 10 is described as follows. When the control circuit 102 receives a horizontal synchronization signal 118 and a vertical synchronization signal 120, the control circuit 102 generates corresponding control signals respectively inputted into the data-line-signal output circuit 104 and the scan-line-signal output circuit 106. The data-line-signal output circuit 104 and the scan-line-signal output circuit 106 then generate input signals to the LCD panel 100 for turning on the corresponding TFTs 114 and changing the alignment of liquid crystal molecules and light transmittance, so that a voltage difference can be kept by the equivalent capacitors 116 and image data 122 can be displayed in the LCD panel 100. For example, the scan-line-signal output circuit 106 outputs a pulse to the scan line 112 for turning on the TFT 114. Therefore, the voltage of the input signal generated by the data-line-signal output circuit 104 is inputted into the equivalent capacitor 116 through the data line 110 and the TFT 114. The voltage difference kept by the equivalent capacitor 116 can then adjust a corresponding gray level of the related pixel through affecting the related alignment of liquid crystal molecules positioned between the two parallel substrates. In addition, the data-line-signal output circuit 104 generates the input signals, and magnitude of each input signal inputted to the data line 110 is corresponding to different gray levels.
Since the physical performance of liquid crystal molecules is similar to a capacitor, the response speed of the liquid crystal molecules may be too slow. In addition, unlike a cathode ray tube (CRT) display applying an impulse-type driving method, an LCD display applying a hold-type driving method has a motion blur phenomenon caused by image edges of a moving subject. In order to reduce the motion blur phenomenon, the prior art provides a black frame insertion technique, or pseudo impulse-type driving technique, to shorten durations of original frames and insert pure black sub-frames or sub-frames with low gray values. In short, the black frame insertion technique inserts a sub-frame with a gray value equal to 0 or a comparative low value between two adjacent frames.
Please refer to FIG. 2 and FIG. 3. FIG. 2 is a schematic diagram of frames of a pixel when performing the prior art black frame insertion technique, and FIG. 3 is a schematic diagram of light intensity generated by the prior art pixel. Shadow areas represent received driving data P0, P1, P2, etc. of the pixel in each frame duration, and the driving data P0, P1, P2, etc. are respectively corresponding to the frame F0, F1, F2, etc. As shown in FIG. 2, gray values of the driving data return to zero (or a comparative low value) before the next driving data is inputted. In such circumstance, variation of the light intensity of the pixel applied the black frame insertion technique is similar to that of a pixel applied the impulse type driving method.
Since the liquid crystal molecules perform as capacitors, the liquid crystal molecules must take time to reach correct gray values when the gray value displayed by the pixel varies. Therefore, although the motion blur phenomenon can be eliminated through the black frame insertion technique, there is a multi-edge effect on edges of the moving subject, especially for a high-contrast image. For example, if a movie shows a bright subject moving in a dark background, the black frame insertion technique can eliminate the motion blur problem in the rear edge of the moving subject. However, in the front edge of the moving subject, the multi-edge effect appears owing to the long response time of the liquid crystal molecules. Similarly, if an animation shows a dark subject moving in a bright background, the black frame insertion technique can eliminate the motion blur problem in the front edge of the moving subject. However, in the rear edge of the moving subject, the multi-edge effect appears owing to the long response time of the liquid crystal molecules.
Therefore, although the prior art black frame insertion technique can eliminate the motion blur problem, there is still the multi-edge effect in an LCD monitor having slow-response liquid crystal molecules. Hence, the image quality of the LCD monitor cannot be enhanced effectively. In addition, as shown in FIG. 3, the pixel displays image data only during half the frame durations, and displays black image with zero gray value during rest frame durations. In other words, the black frame insertion technique shows half the average brightness of original images, and thus affects the image quality.